Nuclear Waste Storage
Introduction:The major problem of nuclear waste is what to do with it. In fact, one of the biggest (and perhaps the single biggest) expenses of the nuclear power industry could eventually be the storage of nuclear waste. Currently there are several ways in which nuclear waste is stored. Most of these methods are temporary. In most cases a viable long-term solution for waste storage has yet to be found. This is because the time period for storage is so incredibly long, on the order of thousands of years.
Temporary Storage of Fuel Rods:
When the spent fuel rods are removed from the reactor core, they are extremely hot and must be cooled down. Most nuclear power plants have a temporary storage pool next to the reactor. The spent rods are placed in the pool, where they can cool down. The pool is not filled with ordinary water but with boric acid, which helps to absorb some of the radiation given off by the radioactive nuclei inside the spent rods. The spent fuel rods are supposed to stay in the pool for only about 6 months, but, because there is no permanent storage site, they often stay there for years. Many power plants have had to enlarge their pools to make room for more rods. As pools fill, there are major problems. If the rods are placed too close together, the remaining nuclear fuel could go critical, starting a nuclear chain reaction. Thus, the rods must be monitored and it is very important that the pools do not become too crowded. Also, as an additional safety measure, neutron-absorbing materials similar to those used in control rods are placed amongst the fuel rods. Permanent disposal of the spent fuel is becoming more important as the pools become more and more crowded.
Permanent Fuel Storage/Disposal:There are many ideas about what to do with nuclear waste. The low-level (not extremely radioactive) waste can often be buried near the surface of the earth. It is not very dangerous and usually will have lost most of its radioactivity in a couple hundred years. The high-level waste, comprised mostly of spent fuel rods, is harder to get rid of. There are still plans for its disposal, however. Some of these include burying the waste under the ocean floor, storing it underground, and shooting it into space. The most promising option so far is burying the waste in the ground. This is called "deep geological disposal". Because a spent fuel rod contains material that takes thousands of years to become stable (and non-radioactive), it must be contained for a very long time. If it is not contained, it could come in contact with human population centers and wildlife, posing a great danger to them. Therefore, the waste must be sealed up tightly. Also, if the waste is being stored underground, it must be stored in an area where there is little groundwater flowing through. If ground water does flow through a waste storage site, it could erode the containment canisters and carry waste away into the environment. Additionally, a disposal site must be found with little geological activity. We don't want to put a waste disposal site on top of a fault line, where 1000 years in the future an earthquake will occur, releasing the buried waste into the environment.
The waste will probably be encapsulated in large casks designed to withstand corrosion, impacts, radiation, and temperature extremes. Special casks will also have to be used to transfer fuel rods from their holding pools and dry storage areas next to the reactor to the permanent geological storage site.
In the US a permanent storage site has been selected at Yucca Mountain, Nevada. Yucca Mountain is in an extremely dry area of Nevada. This minimizes the possibility of water seeping through the rock and corroding the casks. Additionally, if the casks do get corroded, there is not much water flow to carry the nuclear wastes away. The casks will be buried about 1500 feet underground, further preventing the waste from escaping. It is also far from the nearest population center in Las Vegas. While Yucca Mountain is near of a fault line, the fault is believed to be inactive. There are several volcanoes in the vicinity, but scientists believe that they have been dormant for almost a million years and think it unlikely that they will erupt in the next 10,000 years. Naturally, the people in Nevada are opposed to the creation of a nuclear waste repository. They express the common reaction, NIMBY (Not In My Backyard!!). This is because that although most evidence indicates that Yucca Mountain is a suitable place for storage, no one can guarantee that waste will not leak. However, quite a bit of research has already conducted around the Yucca site. Also, work on tunneling into the mountain has been started. The Yucca Mountain Deep Geological Repository is projected to be ready by the year 2010.
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